Acaricidal properties of hemp (Cannabis sativa L.) essential oil against Dermanyssus gallinae and Hyalomma dromedarii

Abstract

The use of conventional pesticides in pest management is facing issues such as developing resistance in pests, environmental pollution and impact on human health, together with regulatory hurdles for approval and marketing of new eco-friendly pesticides to comply with the global trend for residue-free foodstuff. In this framework, botanical pesticides represent valuable alternative products to be exploited. Hemp (Cannabis sativa L.) is an eco-friendly, multipurpose crop that is known for its resistance against insects and parasites. This property is assured by the production of bioactive secondary metabolites such as terpenes and cannabinoids. Notably, the hemp essential oil (EO) contains several terpenoid compounds endowed with pesticide properties. On this basis, in the present work we assayed the toxicity of hemp EO on two ectoparasites of veterinary importance, i.e. Dermanyssus gallinae De Geer and Hyalomma dromedarii Koch. In order to identify the EO chemical constituents responsible for the toxicity on the two ectoparasites, the main monoterpenes and sesquiterpenes of hemp EO, namely α-pinene, myrcene, (E)-caryophyllene and α-humulene were tested as well. Mite contact toxicity assays were carried out at the concentrations of 5, 10, 20, 50, 100 and 200 μg/cm3. Tick larvicidal and ovicidal assays were done testing 0.5, 1, 2, 5, 10, 20, and 50 μg/mL of the hemp EO and its main components. Results from mite contact toxicity showed that hemp EO was toxic to D. gallinae with LC50 values of 47.1 μg/mL. Larvicidal and ovicidal assays revealed the promising activity of the EO against tick larvae and eggs. Among all the tested compounds, (E)–caryophyllene and α-humulene were the most toxic for both ticks and mites, showing LC50 values lower than the whole EO. Myrcene was moderately toxic, with LC50 values higher than the whole EO, whereas α-pinene showed weak acaricidal activity. Taken together our results remarked the potential of hemp EO as a potential botanical acaricide in pest management programs and food production. The industrial scalability is assured by the great availability of land for the cultivation of hemp and its low cost of production.